A launch vehicle is used to launch a payload into orbit around the earth or toward a path outside of earth's orbit. A fairing (also referred to as a payload fairing or a launch vehicle adapter (“LVA”) fairing) is typically used to protect the payload or other portions of the upper stage before and during launch. A payload fairing surrounds the payload in the nose portion of the launch vehicle and a LVA fairing typically surrounds a portion of the spacecraft aft of the LVA or upper stage. The term “fairing” is used herein to reference all types of fairings. The fairing is detachably mounted to the upper stage of the launch vehicle. Once the rocket leaves earth's atmosphere, the fairing is separated from the launch vehicle and discarded to eliminate weight and prepare for separation of the payload. See FIG. 1 showing a launch vehicle 4 (also called a vehicle herein) with two fairings 8A, 8B separated from the spacecraft 12 (also called a payload herein). Each fairing 8A, 8B has a height H, a bottom edge 16 opposite a tip 20, a first axial edge 24 separated from a second axial edge 28 by the bottom edge 16. The fairings 8A, 8B have a half cylinder or an arcuate shape with a partial circumference (i.e., arc length), radius, radius of curvature, an interior surface (also called an inboard surface herein) 32, and an exterior surface (also called an outboard surface herein) 36. The cross-hatching (shading) on the fairings 8A, 8B show the areas of the fairings 8A, 8B that experience the most inward and outward deflection during jettison.
Typically, explosives (e.g., high-energy linear explosive rails), balloons, ballasts, or other force imparting systems are used to separate the two or more payload fairings from each other and from the launch vehicle and to push the payload fairings away from the launch vehicle or spacecraft. FIG. 2A shows a cross-section of the launch vehicle 4 with two fairings 8A, 8B before the fairings 8A, 8B have separated from the spacecraft 12, i.e., at time t0. The fairings 8A, 8B have a width W extending from one edge 24 to the other edge 28. The inner radius R1, R1′ of the fairings at time t0 is shown and is also called the fairing's static inner radius R1, R1′. Dimension R1 corresponds to the edges 24, 28 of the fairing 8A, 8B and dimension R1′ corresponds to the centerline or apex 50 (also called the backbone region) of the fairing 8A, 8B. R1=R1′ at time t0. As the fairings 8A, 8B are jettisoned away from the spacecraft 12, the fairings 8A, 8B first flex or “breathe” outward and away from the spacecraft 12 due to the forces imparted on the fairings 8A, 8B to push the fairings 8A, 8B away from the vehicle 4. This is shown in FIG. 2B by the fairings 8A1, 8B1 in solid lines. FIG. 2B is also a cross-sectional view of the launch vehicle 4 shown in FIG. 2A, but at a later time t1. The solid line fairings 8A1, 8B1 at time t1, just after the fairings 8A1, 8B1 have been jettisoned away from the spacecraft 12, flex or breathe outward as a result of the separation. As each fairing 8A1, 8B1 breathes outward, its inner radius R2 at the edges 24, 28 and its distance from the spacecraft increase compared to that shown in FIG. 2A. Thus, R2 is greater than R1 (R2>R1). Conversely, dimension R2′ corresponding to the fairing centerline or apex 50 decreases compared to dimension R1′. Thus, R2′<R1′. Next, at time t2, the fairing 8A2, 8B2 seeks to return to the natural shape following dissipation of the separation energy. Each fairing 8A2, 8B2, flexes or breathes inward toward the spacecraft 12 as shown by the fairings 8A2, 8B2 in dashed lines in FIG. 2B. The inward breathing of the fairing 8A2, 8B2 reduces the fairing's inner radius R3 to less than the fairing's original static inner radius R1 and increases the dimension R3′ compared to dimension R1′. If the fairings 8A2, 8B2 are not far enough away from the spacecraft 12 at time t2, then the recoiling edges 24, 28 of the fairings 8A2, 8B2 will hit and can damage the spacecraft 12 or vehicle 4.
Prior solutions to the problem of the fairings flexing or breathing inward and hitting the spacecraft or vehicle include ensuring that the radial jettison velocity is large enough that the fairing has separated far enough away to gain clearance to accommodate the recoil or inward breathing of the fairing at the fairing split-line. However, maintaining clearance to the non-jettisoning hardware is challenging. One solution is to increase the energy of the separation explosion to ensure the fairing is sufficiently separated from the spacecraft such that the recoil of the fairing is irrelevant. However, high-energy linear explosive rails create significant vibrations and shocks that can damage components and instrumentation. Similarly, connections based on pyrotechnic strings or explosive bolts are effective and reliable but they generate high levels of vibratory disturbance or shocks which move along the whole vehicle and spacecraft until reaching the most sensitive elements. Mission success of spacecraft, aircraft, and rockets is dependent upon components and instrumentation continuing to operate throughout an entire flight and beyond deployment, for example, in the case of a satellite. Previous attempts also include ballasts added to the split-line in order to achieve the clearance needed. However, these ballasts add significant weight—which is not desired for spacecraft or vehicles. It takes a significant split-line ballast to achieve even a small increase in breathing clearance. In other prior art solutions, supplemental springs are used to increase the clearance distance by modifying the trajectory of the fairing, but the energy per mass and volume in springs is low, and therefore not ideal for applications where weight or space is limited. Additionally, springs can be used to supplement the jettison of a fairing whose primary separating force is a bellows, or the like, or linear explosive assembly. Alternatively, springs can be used as the primary separating force themselves, which will impart less energy into the fairing separation and which generally does not excite the breathing modes as significantly due to springs' lower energy content. However, separation velocity is generally also decreased with springs.
Another existing solution is to decrease the breathing frequency of the fairing by decreasing the stiffness of the fairing in the breathing direction. However, this solution has drawbacks, including a softer, and often heavier, fairing that typically conflicts with other requirements for buckling strength and vibro-acoustics.
Accordingly, there exists a significant and long-felt need for a mechanism that increases fairing jettison clearance without adding significant extra weight and without creating additional vibrations and shocks.